1. Technical Field
The present invention relates to electrophoretic particles, an electrophoretic dispersion liquid, a display sheet, a display device, and electronic equipment.
2. Related Art
In general, it is known that fine particles move (phoresis) in a liquid by Coulomb force when an electric field is applied to a dispersed system to which the fine particles are dispersed in the liquid. This phenomenon is referred to as electrophoresis, and an electrophoretic display device on which desired information (image) is displayed using the electrophoresis has attracted attention in recent years as a new display device.
The electrophoretic display device has a display memory property and a wide viewing angle property in a state in which application of voltage is stopped and a display with high contrast is possible with low power consumption.
Further, the electrophoretic display device is gentle on the eyes when compared to a light emitting type display device, for example, a cathode-ray tube since the electrophoretic display device is a non-light emitting type display device.
In such an electrophoretic display device, a dispersed system (electrophoretic dispersion liquid) in which positively or negatively charged electrophoretic particles are dispersed into a dispersion medium are enclosed between a pair of substrates having an electrode, and the electrophoretic particles migrate to one substrate side and a desired image is displayed by application of a voltage between the pair of substrates (for example, see JP-A-5-173193).
In the related art, for securing dispersibility of the electrophoretic particles in a dispersion medium, an additive, for example, a dispersant, is added to a dispersion medium. However, in a case where an additive is used, it is difficult to reduce power consumption because electrical resistance of a dispersion medium is reduced and a leakage current is increased in a dispersion medium.
For this reason, in the related art, as disclosed in JP-A-5-173193, particles in which the surface of a mother particle is subjected to a treatment using an epoxy-modified coupling agent and then an amino-modified polymer is introduced are known as electrophoretic particles.
In the electrophoretic particles disclosed in JP-A-5-173193, even when the surface of the mother particle itself has a charging property, there is a problem in that the charging property is damaged and becomes insufficient because the entirety of the surface of mother particle is covered with a coupling agent without space. That is, the problem of the electrophoretic particle disclosed in JP-A-5-173193 is that it is difficult to both secure sufficient dispersibility in a dispersion medium and to exhibit desired compatible charging characteristics.
In addition, in the electrophoretic particles disclosed in JP-A-5-173193, even if it is possible to take an advantage of the charging property of the mother particle itself, controlling a charged state while the desired dispersibility is exhibited is difficult because the charging property of the electrophoretic particles highly depends on the charging property of the surface of the mother particle itself. Therefore, in a case where plural kinds of electrophoretic particles with different kinds of mother particles are mixed, the interaction between electrophoretic particles cannot be finely adjusted, so it is not possible to completely resolve coagulation of the electrophoretic particles at the time of applying an electric field. Further, when reactivity between the surface of the mother particle and the coupling agent is considered, the surface of the mother particle has a hydroxyl group in many cases, accordingly, it is difficult to obtain positively charged particles with excellent controllability.